Session Chair: 2013 MRS Fall Meeting

U2: Magnetic Nanostructures and Spin-Electron-Lattice Phenomena in Functional Materials

I will be chairing a technical session at the 2013 MRS Fall Meeting. 

http://www.mrs.org/fall-2013-program-u/

Book Chapter: Parallel Energy Minimizing Computation via Dipolar Coupled Single Domain Nanomagnets

Pulecio, J. F., Bhanja, S., & Sarkar, S. (2013). Parallel Energy Minimizing Computation via Dipolar Coupled Single Domain Nanomagnets. In J. E. Morris & K. Iniewski (Eds.), Nanoelectronic Device Applications Handbook (p. 940). CRC Press. Retrieved from http://www.crcpress.com/product/isbn/9781466565234

2013 MRS Fall Meeting Talk

I will be presenting our work:

 3:30 PM - U2.07 Topological Nature of Magnetic Vortices in Patterned Mesoscopic Disks

Functional magnetic materials have garnered interest due to the potential applications in the emerging field of spintronics. More specifically magnetic vortices have been widely studied due to the quasi-particle/topological nature and are described as having two degrees of freedom, polarity and chirality. While there has been several studies exploring the fascinating behavior of vortices under perturbations using electrical measurements, scanning probe microscopy, and synchrotron based x-ray techniques, transmission electron microscopy provides unparalleled high resolution magnetic and structural information. This allows for a detailed analysis on how the local structure of different materials affects the translation motion of a vortex core under perturbation. Here, we present a direct imaging study of magnetically soft and hard mesoscopic discs of Permalloy and Cobalt under external field perturbations from equilibrium through annihilation and nucleation. The high resolution magnetic imaging of sub 6nm in Lorentz mode affords detail below critical domain wall features of less than 20nm where the soliton-regime breaks down into transverse Bloch walls far from equilibrium. By holding the ferromagnetic system in an external field we can capture the magnetic configuration far from equilibrium states near annihilation and during the nucleation process. Integrating these experiment with micromagnetic simulations we will describe how differently magnetic vortices can behave under perturbations, which is important when attempting to use them in applications such as logic, memories, and antennas. Work supported by the DOE-BES-MSE,under Contract number DE-AC02-98CH10886 .

Congratulations to Joseph Garlow

I want to congratulate my former undergraduate mentee Joseph Garlow who completed his baccalaureate degree in Bio-engineering and is starting his graduate studies in the dept. of Material Science at SBU. He is now formally a PhD student member of our Electron Microscopy and Nanostructure Group, dept. CMPMS @BNL.

During his time under my mentorship Mr. Garlow focused on the growth and characterization of graphene using physcial vapor deposition (PVD) from a solid carbon source. He became well versed in ultra high vacuum technology, electron beam evaporation, scanning electron microscopy, and raman spectroscopy among other things. We are currently working on packaging up this work for peer-reviewed journal publications.

Welcome to the group and I wish you well in your scientific endeavors.

An SEM micrograph of PVD graphene grown on epitaxially grown Ni film (scale bar 5 um). 

Invited Talk: Fundamental Magnetic Interactions in Patterned Nanostructures: Simulation, Fabrication and High-Resolution Microscopy

Thank you to the organizers of  the 2013 MXLS Workshop "New Opportunities for Magnetic Dynamics and Materials at NSLS-II and MAX-IV” for the invited talk.

Fundamental Magnetic Interactions in Patterned Nanostructures: Simulation, Fabrication and High-Resolution Microscopy

Through the use of complimentary multi-technique experimental approaches, investigations of fundamental magnetic interactions, such as magnetostatic, direct exchange, and indirect exchange, in nanomagnetic structures perturbed by static and high frequency excitation, are presented.

Suggestions of using dipolar coupled single domain patterned nanomagnets for applications such as logic, has demonstrated the potential for low-power room temperature operation. The fundamental evolution of reaching desired states can be described as an energy minimization process, where elements exhibit preferential magnetization axes due to engineered shape anisotropies, and local energy minima are reached utilizing external stimuli and strong magnetostatic interactions. Magnetic Force Microscopy (MFM) was implemented in conjunction with NIST’s micromagnetic framework OOMMF, in order to detail the energies associated with different local ground states of coupled nanomangets. The kink energy and magnetic frustrations in ferromagnetic and anti-ferromagnetic ordered elements in various directional applied fields will also be discussed.

Dipolar interactions produce long range force fields but stronger yet are the quantum mechanical short range exchange interactions of neighboring spins. The competing energies of exchange interactions in domain walls and magnetic flux due to surface charges at boundaries can lead to interesting topological charges in room temperature nanomagnetic systems. In a properly engineered nanodisk, magnetic vortices appear, with two degrees of freedom (chirality and polarity), four degenerate states, and exhibit radial symmetry at equilibrium. Utilizing ferromagnetic resonance, transmission electron microscopy, and x-ray transmission microscopy, details of competing direct exchange, demagnetization, indirect exchange energies in magnetic vortex systems are investigated through the observation of core deformation in static fields. The use of high frequency field excitations applied in-situ in TEM to dual vortex core indirect exchange coupled nanodisk heterostructues and the frequency response probed through the time averaged orbital amplitude are also presented. 

APS March Meeting 2013 Talk

I will be presenting our XTM and TEM microscopy work on interlayer exchange couple magnetic vortices under an applied field.

Element Specific Observation of Interlayer Exchange Coupled Dual Vortex Core Nano  Systems

Abstract:

We report on the magnetic evolution of magnetic vortices in nanoscale and multilayer disk structures. The tri-layer structure consists of Co and Permalloy (Py) layers, coupled across a thin (1nm) Cu spacer that provides strong coupling between the Co and Py layers. Element-resolved full-field XMCD microscopy is combined with ultra-high resolution Lorentz transmission electron microscopy, permitting measurement of both layer-resolved domain patterns and the vortex structure averaged across the tri-layer. We examine the evolution of the vortex structure while the nanostructure is cycled through the M-H hysteresis loop. In particular we will discuss the effects of strong interlayer exchanged coupling on a dual vortex core system, including analysis of the layer-resolved coercivity, and the evolution, deformation, annihilation, and nucleation of the vortices.

The figure above shows the domain wall phase diagram measured via Lorentz TEM under quasi-static applied fields.

Introduction to Electron Microscopy

To the class,
It was a pleasure being your instructor. I hope you enjoyed the course and wish you well in your future. I am aware that I may not been able to answer all your questions. Please feel free to ask questions in the comment section below. It may be a similar question(s) that a classmate has and so could be informative to others in this format. All the best.